Fuel burner safety control using flame conduction



y 1954 F. E. CAIRNS, JR 2,684,115

FUEL BURNER SAFETY CONTROL USING FLAME CONDUCTION Filed July 9, 1949 F250 5. cn/elva IN V EN TOR.

prime/V59 shut-off valve 3.

Patented July 20, 1954 FUEL BURNER SAFETY CONTROL USING FLAME CONDUCTION Fred E. Cairns, in, North Hollywood, Calif., assignor to General Controls 00., Glendale, Calif., a corporation of California Application July 9, 1949, Serial N o. 103,767

This invention relates to a burner control for automatically opening a burner valve upon establishment of a pilot flame, and for automatically causing the burner valve to close upon extinguishment of a pilot flame.

This automatic control, in this instance, is effected by utilizing the electric conductivity of a flame; thus, the pilot flame is made a part of an electric circuit that controls the flow of current to an electrically operated valve supplying fuel to the main burner.

It is one of the objects of this invention to utilize the conducting property of the flame in conjunction with an electronic emission device for causing an operative current to flow to the main burner valve.

It is another object of this invention to provide a control system of this character in which the rectifying property of a flame is employed in a simple and effective manner to control the supply of power to an electromagnet.

It is another object of this invention to employ flame conduction for controlling the rate of current flow in an output circuit of an electronic emission device, in which the output circuit includes a reactance that is decreased sharply in value when the flame is in existence.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of one embodiment of the invention. For this purpose, there is shown one form in the drawings accompanying and forming part of the present specification. This form will now be described in detail, illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is defined by the appended claims.

The single figure is a diagrammatic representation of a system incorporating the invention.

In the system shown in the drawing, a main burner l is shown supplied with gaseous fuel from a conduit 2. This conduit 2 is controlled by a Passage of fuel to the main burner I is controlled by an eleetromagnetically operated valve 4.

A pilot burner is arranged in proximity to the main burner l, and is connected to the conduit 2 between the valves 3 and 4. The pilot burner 5 is shown somewhat exaggerated in size in relation to the main burner I.

The electromagnetically operated Valve 4 has a circuit energized by a secondary winding 43 of a transformer 33. The transformer 33 may be 2 Claims. (Cl. 158--123) of the cored type. In this energization circuit are thermostatically operated switching means 25, a limit control switching means 26, and two series connected coil sections ll and 32. The coil sections 4! and 42 are respectively wound upon branch legs of a core of a saturable reactor 40.

A primary transformer winding 34 of the transformer 33 may be connected to a source of alternating current supplied by mains 12. The supply of energy is controlled by a circuit controller 35.

A saturating coil 36 is wound upon the central leg of the core oil. The saturable reactor 4% is such that when its core so is unsaturated, the combined impedance of the coils 4i and 42 is sufliciently high to prevent operation of the electromagnetically operated valve 4. However, when the core 66 is substantially saturated, the reactance oi the coils ill and A2 is reduced, and the valve i may be operated by a substantial alternating current.

saturating current flows through the saturating coil 36 only in the event that a pilot flame i l is in existence. For this purpose, flame electrodes 38 and 3! control an electronic emission device 6, the output circuit of which includes the saturating winding 35.

The electronic emission device 5 includes a cathode 1 indirectly heated by heater 8, an anode 9, and a control electrode Ill. The cathode l of the electronic emission device 6 is connected to an intermediate point of another secondary transformer winding 32 of the transformer 33. One terminal of this winding 32 is connected through the saturating coil 36 to the anode ii. A bypass condenser 39 shunts the coil St. The other terminal of this winding 32 is connected to the control electrode It by way of a high resistance 37. A grid leak condenser 38 bridges this resistance. Energy is transmitted to the secondary winding 32 upon energization of the primary winding 34. The cathode heater 8 is connected across a section of the secondary winding 32.

During a cycle in which the right-hand terminal of the winding 32 is positive, there is a sufficient positive potential impressed upon the anode 9 to permit the passage of a space current. However, the space current is normally controlled by the control electrode H which is maintained at a negative potential. This is efiected because the left-hand terminal or" the winding 32 is negative with respect to the right-hand terminal thereof during this portion of the cycle. During that half of the cycle in which the right-hand terminal of winding 82 is negative, no space curcontrol electrode It.

rent can flow, since the cathode 1 is at a higher potential than the anode 9.

In order to make it possible for current to flow in the output circuit of the electronic emission device 6 and to pass a saturating current through the coil 36 to operate the valve 4, the pilot flame H must be in existence. Under such circumstances, the flame electrodes 38 and ti cause the control electrode to assume a positive potential during that half cycle in which the anode 9 is positive.

For this purpose, the electrodes 30 and 31 are arranged to be in the flame ll and in the direction of flame propagation. Thus, electrode .30 is nearer the root of the flame H, and electrode 3| is nearer the tip. Electrode 30 is directly connected to the control electrode Ii), and theelectrode 3! is similarly directly connected to'the anode 9.

The pilot flame l I, when in existence, provides .a conducting medium to complete .an electrical conducting path between the .anode 3 and the The arrangement of the electrodes 3G and 3! is such that the current flows quite readily through the flame ll fromanode 9 to the control electrode if].

The control electrode 10 then assumes the potential of the anode 9 when the anode is positive. Thus, a rectified current flows between the oathode l and the anode 3 in response to the existence of a pilot flame l i. This space current energizes the saturating coil 35, and the saturation .of the core permits operation-of the valve means 4.

As soon as the flame H is extinguished, either accidentally or otherwise, a conducting medium 1 between electrodes 33 and M is no longer provided, and the potential of the control electrode l6 returns to a negative value whenever the anode is positive. Thus, no substantial current can pass to the saturating winding 36,, and the valve means closes.

Initiation of the operation of the system requires opening of the valve .3 and the closing of the circuit controller 35. Assuming pilot .flame H to be in existence, and the switching devices 25 and 2% closed, the main burner is supplied with fuel and may be lighted by the pilot flame. The limit switch 25 ma be arranged to .open upon a predetermined condition, such as the attainment of a definite pressure or level, or the like, and switch 25 may be caused to respond .to temperature. Forspace heating, the limit switch 26 may be omitted.

What I claim is:

1. In a control system for a main burner and a pilot burner: electrically operated valvemeans for controlling the flow of fuel to .the main burner; first and second electrical transducers, each having an electrical output; a circuit for the electromagnetically operated valve means, including the output of said first electrical transducer, and a reactor coil in .series therewith; a magnetic core for said reactor .coil; .a saturating winding for saturating said magnetic core; the impedance of said reactor coil permitting effective energization of said electromagnetically operated means only when the core is substantially saturated; a circuit for said saturating winding, including the output of saidsecond-electrical transducer and an electronic emission device having a cathode, an anode, and a control electrode, said cathode, anode, and the output of said second transducer being in series with said saturating winding; means forming a biasing circuit for said electronic emission device for normally imposing a bias on said control electrode such as to prevent conduction of current between said anode and said cathode; a. pair of electrodes adapted to project into the flame of said pilot burner and along the direction of flame propagation; a connection between one of said electrodes and said anode; a connection between the other of said electrodes and said control electrode; and means for energizing said transducers.

.2. In a control system for a main burner and a pilot burner: electrically operated valve means for controlling the flow of fuel to the main burner; .a circuit for the electromagnetically operated valve means, including a first transformer winding, and a .reactorcoil in series therewith; a magnetic core for said reactor coil; a saturating winding .for saturating said magnetic core; the impedance of said reactor coil permitting ef-- fective energization of said electromagnetically operated valve means only when the core is substantially saturated; a circuit for said saturating winding, including a second transformer winding and an electronic emission device having a cathode, an anode, and a control electrode, said cathode, anode, and one portion of said second transformer winding being in series with said saturating winding; means forming a biasing circuit for said electronic emission device, comprising a resistor and another portion of said second transformer winding, said resistor and said other portion of said second transformer winding being in series with said cathode and said control electrode for normally imposing a Joias onsaid control electrode such as to prevent conduction of current between said anode and said cathode; a pair of electrodes adapted to project into the flame of said pilot burner and along the direction of flame propagation; a con- .nection between one of said electrodes and said anode; .a connection between the other of said electrodes and :said control electrode; an energizing transformer winding; and means magnetically coupling said energizing transformer winding with said first and second transformer windings.

References Cited ill-17116 ,file of this patent UNITED STATES PATENTS 

